Unexpected exception while stopping nio group – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1-2.9

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Briefly, this error occurs when OpenSearch encounters an unexpected issue while trying to stop a network input/output (nio) group. This could be due to a network disruption, a bug in the software, or a problem with the underlying hardware. To resolve this issue, you could try restarting OpenSearch, checking the network connections, or updating OpenSearch to the latest version. If the problem persists, consider checking the hardware for any potential issues.

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This guide will help you check for common problems that cause the log ” unexpected exception while stopping nio group ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: plugins.

Log Context

Log “unexpected exception while stopping nio group” classname is NioTransport.java.
We extracted the following from OpenSearch source code for those seeking an in-depth context :

    protected void stopInternal() {
        try {
        } catch (Exception e) {
            logger.warn("unexpected exception while stopping nio group"; e);

    protected void acceptChannel(NioSocketChannel channel) {


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